Opportunistic infection (OI) by a variety of organisms represents the most frequent life-threatening manifestation of AIDS. Lacking a cure for the underlying viral infection, effective management of OI is required to sustain a high quality of life for those with AIDS. Infections such as M. avium-intracellular complex (MAI/MAC) are increasingly prevalent in AIDS, and may exacerbate the depression of host resistance to infection. Tissues rich in cells of the reticuloendothelial system (RES) typically contain high concentrations of MAI. At the cellular level, macrophages are replete with undigested intracellular bacteria. MAI is resistant to anti-tuberculosis drugs, and often to a wide range of antibiotics. New pharmaceuticals, optimized formulations, and a detailed understanding of the biology of intracellular parasites are required to attain the short- and long-term goals of control and cure. This research will contribute to the therapy of AIDS-related OI in two ways: (1) explore the cell biology of MAI, to develop new points of therapeutic attack on MAI specifically, and mycobacterial infections generally; (2) improve the effectiveness of therapy, using liposomes, a promising drug carrier system, to target the macrophage reservoir of MAI/MAC. (1) The mechanism by which intracellular parasites evade intracellular degradation is unknown, but important clinically. Intracellular vesicle traffic, phagosome-lysosome fusion, and lysosomal pH may be affected. Novel fluorescence assays, detecting phagocytosis of MAI, vesicular pH, and lysosomal enzyme content have been devised to examine the process of infection. Video fluorescence microscopy and image analysis will show MAI effects on specific compartment of living cells; previous assays often suffer the shortcoming of reporting an average effect on multiple cell compartments, and may hinder study of the true lesion in specific compartments. Understanding the effect of MAI on cellular antibacterial functions may reveal new points for pharmacologic intervention, and allow screening for biological response modifiers that reverse the inhibition of macrophage degradative capacity. (2) Liposomes are undergoing clinical trials as drug carriers for improved therapy of parasitic, fungal, and neoplastic diseases; antibiotics and a variety of biological response modifiers encapsulated in liposomes may be useful for treating OI of P. carinii, M. avium and T. gondii. Strong rationale for liposomes includes efficient natural targeting to the RES site of infection, reduction of adverse effects via site-specific delivery, prolonged lifetime of labile bio-active agents, and improved formulation of active but highly lipophilic drugs. Recent therapeutic experiments show efficacy of antibiotic-containing liposomes against MAI infections in liver and spleen. However, nothing is known of the efficiency with which MAI-infected cells bind and endocytose liposomes. Since endocytosis is required for optimal drug delivery, uptake and intracellular processing of liposomes by infected cells will be examined. Improving therapy of MAI in the lung, using aerosolized or lung-targeted liposomes, is a major objective for later years of the project, since high lung levels of liposomes are achieved by inhalation or intravenous injection.